1. Field of the Invention
This invention relates to a method of forming a coating comprising a pyrolytically formed oxide layer on a travelling hot glass substrate by contacting the substrate with coating precursor material in the presence of oxygen.
2. Background of the Art
It is well known to coat glass for various different purposes. Conductive coatings of various sorts may be applied in order to form part of an electric circuit or to reduce the emissivity of the coated surface in respect of infra red radiation. Reflective coatings for example of a metal may be applied in order to screen solar radiation, as may absorbent coatings.
The invention is particularly concerned with multi-layer coatings in which there is an undercoat of an oxide with one or more superposed layers which may be of oxide or other material.
It is also well known to make multi-layer coatings comprising an oxide undercoat and one or more superposed coating layers. There are various different reasons for applying a multi-layer pyrolytic coating, these having the principal aim of modifying the way in which the upper layer or layers in deposited, or of reducing interaction between the upper coating material and the glass of the substrate and/or of modifying the properties of the total coating, or of reducing interaction between an underlayer of the coating such as the oxide undercoat and atmosphere to protect that underlayer from pollution or indeed from abrasion and so conserve the properties which that underlayer confers on the panel.
It may be useful to prevent interaction between the glass of the substrate and the material of an upper coating layer. As an example, silicon oxide coatings may be used as undercoating layers to be overcoated with other coating layers which may be of one or more different oxides or other materials such as metals. The presence of a silicon oxide undercoating on soda-lime glass has the particular benefit of inhibiting the migration of sodium ions from the glass whether by diffusion or otherwise into an upper coating layer either during formation of that upper layer or during a subsequent high temperature treatment. As an example, it has been found that in the pyrolytic formation of a tin oxide coating from tin chloride on a soda-lime glass substrate, sodium chloride tends to become incorporated into the coating as a result of reaction of the glass with the coating precursor material or its reaction products, and this leads to haze in the coating.
Alternatively, it may be desired to modify the optical properties of a coating which is applied for radiation screening purposes. The radiation screening coatings particularly in view tend to be thin, and accordingly their aspect, whether viewed by transmitted or reflected light, is influenced by interference effects and minor variations in the coating thickness can have an important effect in modifying the apparent colour of the coating. In order to reduce the effect of thickness variations on the apparent colour of the coating, it has been proposed to provide an oxide undercoating, and this can have a highly beneficial effect in reducing undesired interference effects due to variations in the thickness of the total coating, provided that the optical thickness of that undercoat is itself well selected.
Alternatively again, it may be desired to provide an oxide undercoating which confers some special properties on the panel as a whole, and to protect that undercoating by an abrasion resistant coating which also serves to protect to undercoating from chemical attack by the ambient atmosphere.